Mothers who are exposed to particulate air pollution of the fine particles (PM2,5 and PM10) type emitted by vehicles, urban heating and coal power plants are significantly more likely to bear children of low birth weight, according to an international study whose principal authors are Drs. Payam Dadvand and Mark Nieuwenhuijsen, researchers from the Centre For Research in Environmental Epidemiology (CREAL), Barcelona.

The study, the largest of its kind ever performed, analyzed data collected from more than three million births in nine nations at 14 sites in North America, South America, Europe, Asia and Australia.

The researchers found that at sites worldwide, the higher the pollution rate, the greater the rate of low birth weight.

Low birth weight (a weight below 2500 grams or 5.5 pounds) is associated with serious health consequences, including increased risk of prenatal morbidity and mortality and chronic health problems in later life, noted lead author Payam Dadvand, MD, PhD. The study, led by Tracey Woodruff, researcher from University of California (USA), and Jennifer Parker, from the National Centre of Health Statistics, adds that at sites worldwide, the higher the pollution rate, the greater the rate of low birth weight.

“What’s significant is that these are air pollution levels to which practically everyone in the world is commonly exposed,” said Woodruff. “These microscopic particles, which are smaller than the width of a human hair, are in the air that we all breathe.”

Particulate air pollution is measured in size (microns) and weight (micrograms per cubic meter). In the United States, federal regulations require that the yearly average concentration in the air to be no more than 12 µg/m3 of particles measuring less than 2.5 microns.

In the European Union, the limit is 25 µg/m3, and regulatory agencies there are currently debating whether to lower it.

“This study comes at the right time to bring the issue to the attention of policy makers,” said study co-author Mark Nieuwenhuijsen, PhD, of CREAL.
Nieuwenhuijsen observed that particulate air pollution in Beijing, China has recently been measured higher than 700 µg/m3. “From the perspective of world health, levels like this are obviously completely unsustainable,” he said.

Whether these pregnancy exposures can have effects later in life, currently is under investigation through an epidemiological follow-up of some of the children included in these studies.

The study was supported by funds from the Environmental Protection Agency and the National Institute for Environmental Sciences in the United States; the Wellcome Fund in the United Kingdom; and the Ministry of Science and Innovation in Spain.